DINOFLAGELLATE CYST CHANGES AND WINTER ENVIRONMENTAL-CONDITIONS IN VILAINE BAY, SOUTHERN BRITTANY (FRANCE)

During the winter of 1989-1990, changes in dinoflagellate cysts and motile stages were studied respectively in sediment and plankton from Vilaine Bay (South Brittany, France). Special hydrological conditions (decreasing salinities, increased nutrient salts) related to the flood level of the Vilaine River in February 1990 were associated with a considerable increase in dinoflagellates in the water column. Cysts of species with estuarine affinities (Scrippsiella, Gonyaulax) had an elevated experimental germination rate at this time, whereas cysts in sediment were predominantly Brigantedinium sp., Lingulodinium sp. and Spiniferites throughout the study period. A small number of Alexandrium minutum cysts were found in the muddy sediment (maximum of 40 cysts per g-1 of sediment), and the germination rate for this toxic species was also maximal in February.